In recent years, the research and development on so-called energy harvesting (environmental power generation technique) has been widely conducted. In this technique, thermal energy released into the environment from a building, a plant, a motor vehicle, electric products, and the like is converted into electrical energy by a thermoelectric conversion element and utilized as a power supply for driving various sensors, electronic products, and the like which consume relatively low power. Since electric power is obtained as long as thermal energy is released into the environment, the thermoelectric conversion element has the feature of being able to make available low power consumption equipment and the like without caring about power supplies such as cell exchange and charging facilities. Since the thermoelectric conversion element used at present lacks in flexibility, making it difficult to be installed in a waste heat source and a radiation source each having a nonflat shape, and the enlargement of the area of the thermoelectric conversion element for obtaining sufficient energy is difficult, a thin thermoelectric conversion element having high flexibility is desired.
In the thermoelectric conversion element, for example, a P-type thermoelectric element and an N-type thermoelectric element are connected in parallel thermally and in series electrically to take out electric power. In producing the thin thermoelectric conversion element as described above, it is important in terms of the resulting electric power how efficiently a temperature difference can be made across the P-type thermoelectric element and the N-type thermoelectric element in the thickness direction.
In order to efficiently make the temperature difference, PTL 1 discloses a thermoelectric conversion element having a structure as shown in FIG. 6. Specifically, a P-type thermoelectric element 41 and an N-type thermoelectric element 42 are connected in series and thermoelectromotive force takeout electrodes 43 are arranged at both ends thereof to form a thermoelectric conversion module 46. On both surfaces of the thermoelectric conversion module 46 are provided flexible film-like substrates 44 and 45 comprising two types of materials having different thermal conductivity. On the sides of the junction surfaces between the film-like substrates 44 and 45 and the thermoelectric conversion module 46, are provided materials 47 and 48 each having a low thermal conductivity, in which a resin such as polyimide which is an insulator is used as the materials each having a low thermal conductivity. Further, on the opposite sides of the junction surfaces between the film-like substrates 44 and 45 and the thermoelectric conversion module 46, are provided materials 49 and 50 each having a high thermal conductivity so as to be located on a part of external surfaces of the substrates 44 and 45, in which a metal such as copper is used as the material having a high thermal conductivity.